1. Field of the Invention
The present invention relates to DNA assays particularly to the movement and concentration of DNA in microfluidic channels for assays such as amplification and hybridization, and more particularly to a stepped electrophoresis approach using a series of patterned electrodes for moving and concentrating the DNA in a microfluidic channel.
DNA is analyzed for many purposes from obtaining genetic information to identifying pathogens. The manipulation of DNA through microfluidic channels is useful in many assays such of DNA amplification and hybridization. Concentration of DNA at the input to an electrophoresis channel will yield a greater resolution for sequencing.
Electrophoretic channels currently have a single electrode at the input and at the output to move particles down the channels. The resolution of the electrophoretic device is highly dependent on the degree of concentration of the sample at the injection into the channel. Cross-channel injection is sometimes used to provide a small sample but this limits the amount of sample used and thus reduces the signal. Cross channel injection requires a second channel perpendicular to the separation channel and thus increases the amount of space (footprint) needed for injection.
DNA carries a negative charge and thus can be attracted to positively charged electrodes or repelled from negatively charged electrodes. Strong direct current (DC) fields in useful fluids such as water tend to breakdown due to electrolysis. Prior efforts have been directed to moving charged molecules through a medium by the application of a plurality of electric fields of sufficient strength and applied for sufficient amounts of time so as to move the charged molecules through the medium. Such prior approaches are exemplified by U.S. Pat. No. 5,126,022 issued Jun. 30, 1992 to D. S. Soane et al, and by U.S. Pat. No. 5,800,690 issued Sep. 1, 1998 to C. Y. H. Chow et al.
In the present invention a series of electrodes are placed along a fluidic channel and function to move DNA from electrode to electrode by placing a relatively small voltage (<10, preferably <2 between the electrodes. By applying the series of electrodes at the input to the microfluidic channel the sample can be moved sequentially from electrode to electrode to concentrate the sample at the end of the injection region. Thus, a high level of sample can be kept at a concentrated area to increase signal to noise of the device.